P.S. also had this discussion of natural posture. Words like 'natural' have to be used carefully because they often used to refer to two different things. For example, your natural posture is the posture you have at the moment. However through training and being more concsious of your posture it can be improved to produce a 'natural' posture, in that it is the posture which you would have if you hadn't learnt bad behviours of standing/walking. So kata (if done properly)can produce naturalness - or more appropriately, be used to loose unnaturalness.

PPS. that other thread - would agree that aikido DOES NOT come from baby movements. Aikido movements are actually very basic however (can't do difficult motor function movements in a fight) with hands generally moving up and down in front of your body as you move around - thus it just seems like a child because their motor functions are basic.